What happened
On the evening of September 12, 2015, seven hot air balloons gathered at the Mühlau balloon field in Ebnat-Kappel for the 8th International Toggenburg Balloon Days. The event featured a "balloon glow," where crews synchronized burner blasts to music via a wired communication system. During preparations for the Schroeder Fire Balloons G 42/24 (registration HB-QNX), the basket was secured to the ground using a single earth anchor.
At approximately 20:35, the glow event commenced. The pilot and one crew member remained in the basket to manage the burner and vent valve, while two additional crew members stood beside the basket to steady it. As the pilot operated the burner, they frequently pulled the vent line to cool the envelope and prevent an unplanned ascent. During the process, the pilot communicated via radio that additional weight was needed because the cooling efforts were insufficient to maintain stability.
At roughly 20:45, the balloon unexpectedly lifted off. The sudden ascent tore the communication cables connecting the balloons and uprooted the earth anchor. The ground crew released the basket from a height of a few meters and remained unharmed. The balloon ascended to approximately 300 meters, performing several maneuvers over the village of Ebnat-Kappel. After scouting for a landing site, the pilot selected a field at Klösterliweg. After verifying the absence of overhead lines with ground assistants, the pilot used the vent line to descend. The basket struck the ground with a descent rate of approximately 2 m/s, resulting in a hard landing.
The investigation
SUST examined the sequence of events surrounding the unplanned takeoff and the subsequent landing. The investigation focused on the stability of the balloon during the glow event, the effectiveness of the cooling measures taken by the pilot, and the physical forces that led to the failure of the ground anchor.
Findings
- The balloon became too light to be held by the single earth anchor because the pilot could not sufficiently cool the envelope using only the vent valve.
- The unplanned ascent was triggered when the upward lift exceeded the holding capacity of the ground anchor, causing it to be pulled from the earth.
- The landing resulted in one injury, specifically a broken nose sustained by a crew member inside the basket during the impact.